1. Field of the Invention
The present invention relates to a method of fabricating a graphitic carbon film on the surface of a semiconductor and a semiconductor photocatalyst fabricated by the same. In more detail, the present invention relates to a semiconductor of which a substance such as a semiconductor photocatalyst, which has important electrochemical properties, is coated on the surface thereof with a graphitic carbon film having a thickness of 1 nm or less, so as to ensure attenuated electron-hole recombination while keeping the original structure and properties of the semiconductor substance, and a method of fabricating the same.
2. Background Art
Toxic substances (carbon dioxide and nitrogen dioxide, etc.) generated from fossil fuels are the chief culprits in environmental pollution and it is necessary to develop sustainable clean energy sources, with the coming effectuation of the Kyoto protocol which limits the carbon dioxide emission. Using a high-efficiency semiconductor photocatalyst is noted for the fact that it is possible to not only produce an energy source with high energy density, such as hydrogen or methane, from water, but also reuse the water that is a byproduct when using a fuel cell, as a source.
The semiconductor photocatalysts represented by titanium dioxide (TiO2) are used in various fields, for the advantages of chemical stability, low manufacturing cost, and easy storage and distribution, in comparison to organic photocatalysts. The existing semiconductor photocatalysts, however, have a problem in that the photoconversion efficiency is low because electron-hole recombination is frequently generated by various defects in semiconductor substances. It is necessary to improve the problem because only a small amount of photoelectrons generated by light due to the electron-hole recombination, which is a feature of the semiconductors, is used to reduce protons in the external system.
The electron-hole recombination is mainly generated, as the flow of electrons is blocked at the grain boundary created by different atomic arrangement in a polycrystalline substance and at atom vacancies due to non-uniform atomic arrangement. It is necessary to make a high-purity single-crystal semiconductor or form a substance smaller than the electron diffusion length in order to prevent the electron-hole recombination. However, the conditions for forming a semiconductor substance with a high-purity single crystal are very strict and the forming process is complicated, so that it is difficult to use the substance for industrial purposes. In addition, a substance formed with a dimension of several nanometers, which is smaller than the electron diffusion length, has high surface energy, and thereby often exhibit an agglomeration phenomenon, thus this is not considered as an effective solution.
Recently, a study for solving the problem of electron-hole recombination by attaching a substance having high electric conductivity and large capacity to a semiconductor photocatalyst such that the electrons generated from the semiconductor flow to the attached substance has been reported. In particular, graphitic allotropes of carbon represented by fullerenes, CNTs (Carbon Nanotubes), and graphene have been noted because of the abundance of the raw materials and high chemical stability, as well as excellent electrical properties. A study has been reported that when the flow of semiconductor photoelectrons is outwardly induced by binding graphitic allotropes of carbon (fullerenes, CNTs, and graphene) having high electric conductivity and large capacity, the electron-hole recombination phenomenon is reduced and the photoconversion efficiency is increased.
The substances have a problem, however, in that they cannot be applied to semiconductor substances having a complicated structure because the manufacturing method and the forming conditions are restrictive. Therefore, the present invention has been made to provide a method of directly forming a graphitic carbon film on a semiconductor surface having a complicated structure.